1. Field of the Invention
The present invention relates to objective lenses used in optical pickup devices that record information onto and/or reproduce information from optical recording media, such as optical discs, and also relates to optical pickup devices and optical disc apparatuses.
2. Description of the Related Art
In related art, examples of recording media used for information signals are optical discs, such as compact discs (CD) using light beams having a wavelength of about 785 nm and digital versatile discs (DVD) using light beams having a wavelength of about 660 nm, and optical discs that allow for high-density recording by recording signals thereon or reproducing signals therefrom with light beams having a wavelength of about 405 nm using blue-violet semiconductor lasers. Such optical discs that allow for high-density recording will be referred to as high-density-recording optical discs hereinafter. In order to record information signals onto these types of optical discs or reproduce information signals recorded on the optical discs, optical pickup devices are used.
Generally, a single objective lens used in an optical pickup device is preferably designed such that a spherical aberration on an optical path and a paraxial coma aberration are suppressed and a coma aberration occurring due to eccentricity between a first surface and a second surface of the lens is also suppressed. In optical systems with high numerical aperture and short wavelengths that have been developed with the increase in density in optical discs, the occurrences of spherical aberration on the optical path and paraxial coma aberration are minimized in view of design. Moreover, the eccentricity is minimized by strictly maintaining the fabrication precision and adjustment precision during the fabrication process so that a coma aberration occurring due to eccentricity can be suppressed.